Diamond is outstanding for field use. It will abrade (notch or smooth) any hard material, so it often becomes a problem solver for things other than sharpening.

When weight becomes an issue, I have used both DMT and EZLap diamond stones, which come mounted on a plastic slab. These are monocrystalline diamond, which lasts a LOT longer than the Chinese polycrystalline ones (the latter are perfectly fine for occasional use). I tend to go with a medium grit for its versatility, even though it creates a coarser edge.

In everyday use, the diamond file on the WaveII is the go-to tool. It is an excellent thing to have at hand. (And the uninitiated are always impressed when you whip out a chunk of "industrial diamond" and solve the problem on the spot.)